When a human comes into a projection light path between a projector for projecting an image onto a screen and the screen and turns his or her face toward the projecting side, there is a danger in that the projection light may stimulate his or her eyes. Therefore, a method has been proposed in which a detection section for detecting the presence or absence of an object in the projection light path and a control section for controlling radiation power are provided in an image display apparatus, and when an object is detected in the projection light path, the radiation power is reduced to prevent danger.
For example, Patent Document 1 discloses an image display apparatus which monitors a projection region with an electromagnetic radiation sensor, a thermal radiation sensor, a pyroelectric sensor, a temperature sensor, or the like, and when an object exists in the projection region, switches to an operation mode which is made harmless to humans.
Moreover, Patent Document 2 discloses an image display apparatus which monitors a projected image with a camera, extracts a region in which a human is present, and causes any image to be masked in that region. With this apparatus, the radiation power only needs to be limited in the region where human presence is determined within the projection region, thus permitting an image to be still displayed in any other region.
Moreover, an image display apparatus which projects laser light to display an image (also referred to as a laser projector) is under development. Laser light which is output from a laser light-emitting element has a higher color purity than that of light which is output from a lamp, and thus allows for an improved color reproduction. In addition, the optics can be downsized and also the power consumption can be reduced, so that an image display apparatus can be realized which is power-thrifty and small-sized.
Since laser light is available for scanning in a thinly constricted state, a mirror element or the like can be used to perform a two-dimensional scanning with laser light, whereby an image is displayed. Such a scanning-based laser projector displays an image by modulating the intensity of laser light, and thus is even more power-thrifty than any usual projector that uses two-dimensional image displaying devices, e.g., a liquid crystal panel or a DMD (Digital Micromirror Device). Moreover, downsizing of the apparatus can also be achieved because there is no need for illumination optics for uniformly illuminating two-dimensional image devices.
Thus, a scanning-based laser projector is mountable even in a small-sized mobile device. Thus, large-scale displaying can be enjoyed even with a mobile phone or the like, in which a large-sized display would be difficult to be mounted.
In a scanning-based image display apparatus that uses a beam which is thinly constricted by a scanning means such as a mirror device, other than ensuring safety by detecting the presence or absence of an object intruding the projection light path, it is also necessary to provide safety measures in case of an unintentional halting of the mirror ed. Therefore, an approach has been proposed which detects the scan operation of the mirror, and in a state of abnormal scan operation, blocks the laser light or cuts supply of electric power to the laser light source.
For example, in Patent Document 3, the mirror is halted and retained at a predetermined position when the scan operation of the mirror is not normal, e.g., in the case where the scan operation is completely halted, or where the period is not constant and the speed is not as predetermined. At this time, the laser light is allowed to be radiated onto a light shielding portion so as not to be radiated outside the image display apparatus, thus being blocked from going outside.
In Patent Document 4, electric power is supplied in synchronization with the pivoting of the mirror, and supply of electric power to the laser light source is cut when the scan operation of the mirror is not normal, e.g., in the case where the scan operation is completely halted, or where the period is not constant and the speed is not as predetermined.    [Patent Document 1] Japanese Patent No. 2994469    [Patent Document 2] Japanese Laid-Open Patent Publication No. 2004-254145    [Patent Document 3] Japanese Laid-Open Patent Publication No. 2004-312347    [Patent Document 4] Japanese Laid-Open Patent Publication No. 2004-333698